Vibration isolation tables are used for supporting highly sensitive equipment, such as optical and analytical devices, on a substantially vibration free surface. Simple forms of these tables are well known and generally include a range of designs from thick granite to a tabletop comprising metallic upper and lower surfaces with connecting sidewalls. The upper surface of the tabletop typically contains a plurality of holes, usually drilled and tapped, that are used for securing equipment, such as optical equipment and the like, upon the upper or lower surfaces of the tabletop. For the most part, these tabletops are manufactured from extremely heavy materials and, when assembled, are heavy, bulky, and difficult to move or reposition. These tabletops are often supported by a vibration isolation system. An example of a vibration isolation system used with such a table would be the isolation system described in U.S. Pat. No. 4,360,184.
There have been some attempts to reduce the weight of these tables without a loss of structural strength. Previously a honeycomb core has been incorporated into these tables, with or without additional stiffening or damping components, which maintains a rigid separation between the top and bottom surfaces and therefore increasing the structural integrity of the tabletop while reducing the overall weight. These tabletops are commonly referred to as honeycomb tabletops. The honeycomb tabletop is an efficient structure for providing an array of tapped holes while also meeting the needs of flatness, and reasonable weight.
These tabletops need to be very heavy in order to reduce the vibratory effects of individuals brushing up against them, mechanical movement of instruments placed upon them, and/or external vibration sources. However, their heavy weight makes them difficult to move and/or reposition conveniently. Indeed, many optical tables, once positioned, are never again repositioned due to the great effort and expense required.
Thus, there is a need for a variable mass platform that is constructed in such a way that the overall mass of the table top may be varied as needed, from lightweight for movement and repositioning to heavyweight for vibration dampening and stability. Further, there is a need for a variable mass platform that also allows the user to "tune" the resonant null frequency of the platform to optimize the vibration signature with various pieces of equipment mounted on the table.